The present invention relates to a production method of an anisotropic conductive film and an anisotropic conductive film produced by this method.
Anisotropic conductive films have been widely used in the electronic industry as a connector for testing semiconductor devices and circuit boards, a connector of circuits between boards, a material for mounting a semiconductor device on a circuit board and the like. A known anisotropic conductive film is formed by dispersing conductive particles in a film made from an adhesive insulating resin. However, this anisotropic conductive film is subject to restriction because a fine pitch connection is difficult to achieve and a convex terminal (e.g., bump contact) is required as a connection terminal of a semiconductor element.
To solve this problem, the Applicant proposed, in WO98/07216 etc., an anisotropic conductive film having plural conductive paths insulated from each other and penetrating an insulating film substrate in the thickness direction of the film substrate. The proposed anisotropic conductive film contains plural conductive paths with both ends exposed on the surface of the film substrate made from an insulating resin, and, of these plural conductive paths, those located at the positions allowing contact with the termini of an object to be electrically conducted afford electrical continuity with this object.
However, a close study of the physical properties and the connection state of the connection mate of the anisotropic conductive film proposed above has revealed that the conductive path (metal conductor) in the film has a density higher than necessary, making the film hard to deform, which in turn tends to lower the follow-up property of the film to the connection target (particularly in the case of testing connectors, the degraded follow-up property of the film to the test target sometimes necessitates hard pressing of the film with a high pressure to bring a conductive path in contact with a terminal (electrode) of the test target), and that the density of the conductive path (metal conductor), which is higher than necessary, makes the amount of the insulating resin insufficient to provide an adhesive property when used as a material for mounting, thereby preventing sufficiently high adhesion to an object to be connected.
The above-mentioned conventional anisotropic conductive film is produced by winding plural insulated wires (metal conductor wires having a coating layer made from an insulating resin) around a core member to give a multi-layer roll with the insulated wires densely packed both in the longitudinal direction and the transverse direction, adhering coating layers to make the densely packed insulated wires inseparable, and slicing each insulated wire along the plane forming an angle with the wire section to give a film having a conductive path made of the metal conductor wires. By making thicker the coating layer of the insulated wire to be wound around the core member, the interval of the metal conductor wires (conductive paths) can be widened, which in turn lowers the density of the conductive paths in the film to some degree. While the coating layer can be made thick by repeat coating the metal conductor wires with an insulating resin, the cost necessary for this step is not small at all and the step is impractical. In addition, it is not that the thickness of the coating layer can be increased to any desired level, and the interval of the metal conductor wires (conductive paths) cannot be widened sufficiently. On the other hand, a comparatively large clearance may be formed between adjacent insulated wires when bundling the plural insulated wires and the coating layer of the insulated wires may be melted to widen the interval of the metal conductors. In this case, however, unnecessary voids are formed between the metal conductor wires in the film, thus lowering the strength of the film to the extent that it is not practicable.
It is therefore an object of the present invention to provide a production method of an anisotropic conductive film, which is capable of sufficiently widening the interval (pitch) of the centers of conductive paths without forming unnecessary voids in the film.
It is also an object of the present invention to provide an anisotropic conductive film, which has a sufficient strength and deformability, which shows fine follow-up property to an object to be connected, which is capable of connecting a conductive path to a terminal (electrode) of a test object with a low pressure, when used for testing connectors, and which can form a highly reliable electrical connection by firmly adhering to an object to be connected, when used as a mounting material.
It has been also found that an anisotropic conductive film free of unnecessary voids in the film, having a sufficiently large pitch of conductive paths (metal conductors), and having a decreased density of the conductive paths can be obtained by forming a laminate comprising alternate layers of a winding layer comprising a single row of insulated wires, and an insulating resin film, which laminate being made by placing an insulating resin film on the winding layer comprising the insulated wire wound around a core member, and cutting this laminate to give a film.
Accordingly, the present invention provides the following.
(1) A production method of an anisotropic conductive film, which method comprises the steps of
(a) winding an insulated wire around a core member to form one roll of a winding layer, said insulated wire comprising a metal conductor wire and a coating layer made from an insulating resin, which coating layer being formed on said wire, placing an insulating resin film on the obtained winding layer, and repeating the winding and the placing to give a laminate alternately having the winding layer comprising a single row of insulated wires and an insulating resin layer made from the insulating resin film,
(b) partially or entirely melting at least one of the coating layer and the insulating resin layer to integrate the winding layer and the insulating resin layer, and
(c) slicing the laminate along a plane forming an angle with the insulated wire in a desired film thickness.
(2) The production method of the anisotropic conductive film of the above-mentioned (1), wherein the insulated wire is wound around the core member in such a manner that a space is formed between one winding and the next winding of the insulated wire.
(3) The production method of the anisotropic conductive film of the above-mentioned (1) or (2), wherein a winding position of the insulated wire in odd-numbered winding layers and a winding position of that in even-numbered winding layers, as counted from the core member, are different from each other in the longitudinal direction of the core member.
(4) The production method of the anisotropic conductive film of the above-mentioned (1), wherein the coating layer of the insulated wire and the insulating resin film are made from the same kind of resin.
(5) The production method of the anisotropic conductive film of the above-mentioned (1), wherein the insulating resin film has a multilayer structure.
(6) The production method of the anisotropic conductive film of the above-mentioned (5), wherein the insulating resin film comprises at least one surface layer, which comes into contact with the coating layer of the insulated wire, and which softens and flows to be able to adhere to the coating layer of the insulated wire at a temperature at which the layers other than the surface layer do not soften.
(7) The production method of the anisotropic conductive film of the above-mentioned (5), wherein the film having the multilayer structure comprises at least one surface layer, which comes into contact with the coating layer of the insulated wire, and which has a softening point lower by 20xc2x0 C. or more than the softening point of the layers other than the surface layer.
(8) An anisotropic conductive film produced by the production method of the above-mentioned (1), which comprises a band area A comprising a first insulating resin layer and plural conductive paths, the conductive paths being insulated from each other, arranged in one row and penetrating the first insulating resin layer in a layer thickness direction, and a band area B comprising a second insulating resin layer without a conductive path, wherein the band areas A and the band areas B are alternately melt-adhered to form the film.
(9) The anisotropic conductive film of the above-mentioned (8), wherein the plural band areas A each comprise a row of conductive paths, the rows of the conductive paths being arranged in parallel, and two band areas A sandwiching one band area B are disposed at a distance of 2.5-10 times the diameter of the conductive path as measured between the centers of the conductive paths of two band areas A.
(10) The anisotropic conductive film of the above-mentioned (8), wherein the first insulating resin layer of the band area A and the second insulating resin layer of the band area B are made from the same kind of resin.
(11) The anisotropic conductive film of the above-mentioned (8), wherein the second insulating resin layer of the band area B has a multilayer structure comprising plural layers laminated in the width direction thereof, and at least one layer on the side that comes into contact with the first insulating resin layer of the band area A softens and flows to be able to adhere to the first insulating resin layer at a temperature at which the layers other than this layer do not soften.
(12) The anisotropic conductive film of the above-mentioned (11), wherein, of the plural layers constituting the second insulating resin layer of the band area B, at least one layer on the side that comes into contact with the first insulating resin layer has a softening point lower by 20xc2x0 C. or more than that of the layers other than the surface layer.
(13) The anisotropic conductive film of the above-mentioned (8), wherein the film contains a conductive path in a proportion of volume of 1-30%.